Occupant presence detection is frequently used in connection with air bags and other pyrotechnically deployed restraints as a means of determining if the restraints should be deployed in the event of sufficiently severe crash. One commonly employed way of detecting occupant presence involves installing a fluid-filled bladder in or under the bottom foam cushion of the vehicle seat and measuring the fluid pressure in the bladder with a pressure sensor. Exemplary systems of this type are disclosed, for example, in the U.S. Pat. Nos. 5,987,370 and 6,246,936 to Murphy et al., and the U.S. Pat. Nos. 6,101,436 and 6,490,936 to Fortune et al., all of which are assigned to Delphi Technologies, Inc., and incorporated herein by reference.
In a somewhat different approach, the cost of the pressure sensor can be avoided by providing conductor plates on or near the upper and lower surfaces of a fluid-filled bladder, and detecting changes in capacitance between the plates when the thickness of the bladder changes due to the presence of occupant weight. See, for example, the U.S. Pat. No. 6,927,678 to Fultz et al., assigned to Delphi Technologies, Inc. and incorporated herein by reference.
In yet another approach, the upper and lower plates of a capacitive sensor are separated by a layer of foam or other compressible material instead of a fluid-filled bladder. See, for example, the U.S. Pat. No. 6,999,301 to Sanftleban et al. and the U.S. Patent Application Publication No. 2006/0196702 to Hansen et al., both of which are assigned to Delphi Technologies, Inc., and incorporated herein by reference.